spamassassin and amavisd with stock sendmail

[Eric Melville]

I've got a very plain and standard sendmail configuration running on a
machine as a primary mail exchanger. After years of running without any
kind of automated spam filtering, it's just gotten too poor and I have
to turn to rejecting mail.

I installed the spamassassin and new-amavisd port, set the basic
configuration options, turned them on, and it doesn't seem to do anything.
My "test" has been to tell it to tag messages even with a threshold of
zero, and nothing is ever tagged.

Has anyone got a walk through or good document on getting these tools
running on FreeBSD with the system's base sendmail installation? I've
tried web searching and my usual FreeBSD documentation sites with no
luck so far.